U.S. patent number 4,882,574 [Application Number 07/209,360] was granted by the patent office on 1989-11-21 for two-resistor ice detector.
Invention is credited to Boris Khurgin.
United States Patent |
4,882,574 |
Khurgin |
November 21, 1989 |
Two-resistor ice detector
Abstract
An ice detector comprises first and second simultaneously
electrically energized resistors one of which is in good thermal
contact with the surface where the presence or absence of ice is to
be detected and the other of which is thermally insulated from that
surface. When ice is present on that surface there will be a
different between the temperatures, and hence the resistances, of
the two resistors, which difference, when sensed, indicates the
existence of ice.
Inventors: |
Khurgin; Boris (New York,
NY) |
Family
ID: |
22778468 |
Appl.
No.: |
07/209,360 |
Filed: |
June 20, 1988 |
Current U.S.
Class: |
340/581;
340/580 |
Current CPC
Class: |
B64D
15/20 (20130101) |
Current International
Class: |
B64D
15/20 (20060101); B64D 15/00 (20060101); G08B
021/00 () |
Field of
Search: |
;340/581,580 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: James & Franklin
Claims
I claim:
1. An ice detector comprising first and second
temperature-sensitive resistors, means for mounting said first
resistor in good thermal conductivity with respect to a surface
where the presence or absence of ice is to be detected, means for
mounting said second resistor in good thermal insulation with
respect to said surface, means for simultaneously electrically
energizing said resistors, and means for detecting a difference in
the resistance of said resistors after they have been energized and
activating an indicator in response to a predetermined resistance
difference, thereby indicating the presence of ice on said
surface.
2. An ice detector comprising first and second
temperature-sensitive resistors of substantially equal resistance,
means for mounting said first resistor in good thermal conductivity
with respect to a surface where the presence or absence of ice is
to be detected, means for mounting said second resistor in good
thermal insulation with respect to said surface, means for
simultaneously electrically energizing said resistors substantially
equally and means for detecting a difference in the resistance of
said resistors after they have been energized and actuating an
indicator in response to a predetermined resistance difference,
thereby indicating the presence of ice on said surface.
3. The ice detector of either of claims 1 or 2, in which said
resistors are electrically connected to one another and to other
resistors to form a bridge circuit, said energizing means
energizing said bridge, said detecting means being sensitive to the
resistance of the elements of said bridge.
4. An ice detector comprising a housing having a surface where ice
detection is to take place, first and second temperature-sensitive
resistors mounted in said housing, said first resistor being so
mounted as to be in good thermal conductivity with said surface,
said second resistor being so mounted as to be thermally insulated
from said surface, means for simultaneously electrically energizing
said resistors, and means for detecting a difference in the
resistance of said resistors after they have been energized and
activating an indicator in response to a predetermined resistance
difference, thereby indicting the presence of ice on said
surface.
5. An ice detector comprising a housing having a surface where ice
detection is to take place, first and second temperature-sensitive
resistors of substantially equal resistance mounted in said
housing, said first resistor being so mounted as to be in good
thermal conductivity with said surface, said second resistor being
so mounted as to be thermally insulated from said surface, means
for simultaneously electrically energizing said resistors, and
means for detecting a difference in the resistance of said
resistors after they have been energized and activating an
indicator in response to a predetermined resistance difference,
thereby indicating the presence of ice on said surface.
6. The ice detector of either of claims 4 or 5, in which said
resistors are electrically connected to one another and to other
resistors to form a bridge circuit, said energizing means
energizing said bridge, said detecting means being sensitive to the
resistance of the elements of said bridge.
7. The ice detector of claim 6, in which said resistors are
electrically connected to one another and to other resistors to
form a bridge circuit, said energizing means energizing said
bridge, said detecting means being sensitive to the resistance of
the elements of said bridge.
8. The ice detector of claim 6, in which that portion of said
housing defining said surface is of poor thermal conductivity, said
first resistor being mounted in said portion so as to be thermally
operatively exposed at said surface and said second resistor being
located in said portion remote from and thermally insulated from
said surface.
9. The ice detector of any of claims 1, 2, 4 or 5 in which at least
said first resistor is substantially surrounded by a body of
electrically insulating material of good thermal conductivity.
10. The ice detector of claim 9, in which said resistors are
electrically connected to one another and to other resistors to
form a bridge circuit, said energizing means energizing said
bridge, said detecting means being sensitive to the resistance of
the elements of said bridge.
11. The ice detector of any of claims 1, 2, 4 or 5 in which at
least said first resistor is substantially surrounded by a body of
electrically insulating material of good thermal conductivity which
is in turn substantially surrounded by a substantially rigid body
of good thermal conductivity.
12. The ice detector of claim 11, in which said resistors are
electrically connected to one another and to other resistors to
form a bridge circuit, said energizing means energizing said
bridge, said detecting means being sensitive to the resistance of
the elements of said bridge.
13. The ice detector of any of claims 1, 2, 4 or 5 in which at
least said first resistor is surrounded by a layer of electrical
insulation sufficiently thin as to place said resistor in good
thermal conductivity with the outside of said layer.
14. The ice detector of claim 13, in which said resistors are
electrically connected to one another and to other resistors to
form a bridge circuit, said energizing means energizing said
bridge, said detecting means being sensitive to the resistance of
the elements of said bridge.
15. The ice detector of any of either of claims 4 or 5 in which
that portion of said housing defining said surface is of poor
thermal conductivity, said first resistor being mounted in said
portion so as to be thermally operatively exposed at said surface
and said second resistor being located in said portion remote from
and thermally insulated from said surface.
Description
This invention relates to means for indicating the presence or
absence of ice on a surface.
BACKGROUND OF THE INVENTION
There are many instances when it is important to know whether, or
to what extent, ice has formed on a given surface. The presence of
ice on the wings, control surfaces or fuselage of aircraft is known
to be potentially life threatening, but there are many other
instances (e.g., cooling towers, aerials, refrigerator elements,
bridges and roadways and the like) where ice detection is also
important. While various procapable of detecting ice formation and
indicating when ice has formed to an impermissible degree, in
general those prior art devices suffer from complexity,
expensiveness and unreliability. In many instances they are also
undesirable for use with aircraft because they normally project out
from the aircraft surface where ice detection is to take place and
therefore disturb the aerodynamic efficiency of the craft. For
example, the device disclosed in Bullen et al. U.S. Pat. No.
2,803,813 of Aug. 20, 1957 utilizes an element which normally
projects beyond the aircraft surface so that if icing conditions
prevail ice can form on that object, as a result of which when the
object is pulled back into the aircraft its retrograde motion will
be impeded by the ice and thus will cause a part within the housing
to move and actuate an alarm. In addition to the fact that the part
must project out from the airplane for an appreciable period of
time in order to give ice the opportunity to form on it if weather
conditions are appropriate, the presence of foreign particles other
than ice on the exterior of the object will cause false alarms,
thus making it unreliable.
SUMMARY OF THE INVENTION
The ice detector of the present invention not only does not have
any parts projecting from the aircraft surface at any time, thus
never interfering with proper air flow over that surface, but has
no moving parts at all. It is electrical in nature, and is positive
in operation, not requiring reference voltages or stabilized
currents. It is designed to indicate the presence or absence of ice
periodically, at a time frequency appropriate to the external
conditions. For example, tests may be made only upon command, or
once a minute or once every ten minutes or, if the situation is
potentially critical, once every fraction of a minute.
It is the prime object of the present invention to devise an ice
detector which is inexpensive, positive and reliable in operation,
and adaptable to many different requirements.
It is a further object of the present invention to devise such an
ice detector which in no way interferes with the normal aerodynamic
functioning of the aircraft in which it is installed.
It is yet another object of the present invention to devise such an
ice detector which performs its act of detection quickly and
positively and then resumes a standby condition, ready to perform
its ice detection function at any desired later time.
It is a still further object of the present invention to devise an
electrically energized ice detector which is inherently accurate
and reliable, and which is not dependent upon precision in its
electrical sources.
To these ends the ice detector of the present invention comprises a
pair of resistors whose temperature-resistance characteristics are
known and are preferably similar. One of those resistors is mounted
so as to be in good thermal connection with the surface where ice
is to be detected and the other of those resistors is mounted so as
to be thermally insulated from that surface. During the detection
cycle the two resistors are simultaneously electrically energized,
and the passage of current therethrough will cause their
temperatures to rise and that in turn will cause their resistance
to increase. Since the first resistor is in good thermal
conductivity with the surface in question, the presence of ice on
that surface will cause the temperature of the first resistor to
remain constant or to increase more slowly than if ice were not
present on that surface, whereas the presence or absence of ice on
that surface will have no effect on the rate of temperature
increase, and hence the rate of resistance increase, of the second
resistor. Thus if no ice is present the relationship between the
resistances of the two resistors after they have been electrically
energized for a predetermined period will be different than if ice
is present on that surface. When the two resistors are initially of
the same resistance and have the same temperature coefficient of
resistivity, as is preferable, the resistances of the two resistors
will remain the same if no ice is present but will differ if ice is
present. The difference between the resistances of the two
resistors is detected, and when that difference reaches a
predetermined magnitude an appropriate alarm or indicator is
actuated to indicate the presence of ice on the surface to be
monitored. Detection of this resistance difference is greatly
facilitated if the two resistors are connected in a bridge circuit
with other resistors, this eliminating the need for any reference
voltage sources and permitting the system to function accurately
even though the source of electrical energy may not be
constant.
BRIEF DESCRIPTION OF THE DRAWING
To the accomplishment of the above, and to such other objects as
may hereinafter appear, the present invention relates to the
construction and operation of an ice detector as defined in the
appended claims and as described in this specification, taken
together with the accompanying drawings, in which:
FIG. 1 is an idealized view showing one application for the ice
detector of the present invention, to wit, to detect the presence
of ice on the skin of an aircraft;
FIG. 2 is a cross-sectional view of a preferred embodiment of the
present invention showing the device in place on the aircraft
skin;
FIG. 3 is a view similar to FIG. 2 but of an alternative
embodiment; and
FIG. 4 is a circuit diagram of one way in which the ice detector of
the present invention can be used.
DISCLOSURE OF THE PREFERRED EMBODIMENTS
While I have here chosen to illustrate the device of the present
invention as used to detect ice on the skin of an aircraft (the
device generally designated A in FIG. 1 being mounted inside an
aircraft adjacent to the skin thereof), that being a very important
application for the detector of the present invention, it will be
understood that is by way of illustration only, and that my ice
detector can be used in many other environments where detection of
the presence or absence of ice is called for.
In FIG. 2, illustrating a preferred embodiment of the present
invention, the ice detector A comprises a housing generally
designated 2 secured to the inside of a mounting structure 4, such
as the skin of an aircraft, by screws 6 so as to have its forward
portion 8 extend snugly into an opening 10 in the skin of the
structure 4. Preferably the forward surface 14 of the housing 2
will then be flush with the outer surface 12 of the skin 4, so that
the detector in effect constitutes a continuation of the outer
surface of the skin of the aircraft and therefore does not
interfere at all with the aerodynamic functioning of the aircraft
structure. The housing 2 is formed of any suitable structural
material, but with at least a portion of that housing 2, and
preferably the entire housing, being formed of a material which is
a good thermal insulator. It may, for example, be comprised of
asbestos together with some rigidifying impregnant if desired.
Mounted within the housing 2 are first and second electrical
resistors 16A and 16B respectively, each having leads 18A and 18B
respectively extending therefrom to the exterior of the housing 2.
In the embodiment disclosed in FIG. 2 the resistors 16A and 16B are
embedded in bodies 20A and 20B respectively formed of a material
which is a good electrical insulator and which has a high thermal
conductivity. One such material is that which is sold by Stockwell
Rubber Company under the trademark "Coolsil", and which is
currently used as a heat sink material in various electronics
applications. The bodies 20A and 20B are surrounded by rigid bodies
22A and 22B respectively of good thermal conductivity, for
instance, copper.
The first resistor 16A, with its associated surrounding bodies 20A
and 22A, is mounted within a recess 24 in the housing 2 which is
open at the surface 14, and the upper surface of the body 22A is
preferably there exposed. As a result, because both of the bodies
20A and 22A are of high thermal conductivity, the resistor 16A will
be in good thermal conduction with the surface 14. By way of
contrast, the second resistor 16B, with its associated bodies 20B
and 22B, is entirely encased within the housing 2, separated from
the surface 14 by a portion 2A of the housing 2 of sufficient
thickness, and with a sufficiently high thermal insulation
characteristic, so that the resistor 16B is thermally insulated
from, and is essentially not sensitive to thermal conditions at,
the surface 14.
FIG. 4 represents a preferred circuit arrangement for using the
resistors 16A and 16B to detect the presence or absence of ice at
the surfaces 12 and 14. Those two resistors, which are preferably
the same in nominal resistance and with essentially the same
temperature-resistance coefficient, are connected to one another
and to two reference resistors 16C and 16D in the manner shown to
form a typical Wheatstone bridge B, with resistors 16A and 16B
being in series with one another and in parallel with
series-connected resistors 16C and 16D. A power supply 26
controlled by a timer and/or manual control 28 is connected across
bridge nodes 30 and 32, while an amplifier 34 is connected across
bridge nodes 36 and 38, the nodes 36 and 38 being located between
resistors 16A and 16B and resistors 16C and 16D respectively, while
the nodes 30 and 32 are connected between resistors 16A and 16C and
between resistors 16B and 16D respectively. The amplifier 34 is
connected, preferably by means of Zener diode 40, to an alarm or
indicator 42.
An alternative structural embodiment of the detector of the present
invention is disclosed in FIG. 3. There each of the resistors 16A
and 16B is covered by a thin layer 40A and 40B respectively of an
electrical insulator, the layer being thin enough so as to place
the resistors in good thermal connection with their surroundings.
Typically the resistors may be made of nickel covered by an
electroplated layer of copper of perhaps 0.001" thickness, with the
outer surface of that copper then being oxidized to produce a layer
of copper oxide, such as that known by the trade name "Melaconite".
As will be apparent from FIG. 3, resistor 16A will therefore be in
good thermal connection with the surface 14 while the resistor 16B
will be thermally insulated therefrom.
Although the elements 16A and 16B have been here generically
referred to as resistors, it is preferred that they be in the
nature of electrical heating elements which, when electrically
energized, produce a substantial amount of heat, to the end that
when those elements are electrically energized the significant
amounts of heat produced thereby will tend to cause their
temperatures to increase relatively rapidly and, as is well known,
when resistors increase in temperature their resistance increases.
It is preferred that the elements be formed of material which has a
relatively high temperature-resistivity coefficient, thereby to
produce significant changes in resistance as the temperatures of
the elements change.
The Zener diode 40 is provided to prevent actuation of the alarm or
indicator 42 unless and until the output amplifier 34 reaches a
predetermined value, thus minimizing the possibility of false
alarm.
Since the two resistors may be at different temperatures under
normal standby conditions--the air to which resistor 16A is exposed
may be quite cold--and hence exhibit different resistances when
energized, and since the bridge B must nevertheless be balanced in
the absence of ice, the resistor 16C may be made adjustable to
achieve that bridge balance under those ice-free conditions. When
no ice 44 is present the temperatures of the two resistors will
continue to present the same temperature difference even though
both resistances change, so the bridge B will remain balanced, but
if ice 44 is present the heat from resistor 16A will largely go
toward melting that ice before the temperature of that resistor 16A
can rise, and hence the temperature difference (and resistance
difference) between the two resistors will increase, unbalancing
the bridge B and actuating the alarm or indicator 42.
The adjustability of resistor 16C and/or 16D can also be used to
advantage to compensate for any differences in resistance of
resistors 16A and 16B when they are at the same temperature.
When the device of the present invention is to be used to detect
the presence or absence of ice at the surfaces 12 and 14 the
control or timer 28 will actuate the power source 26 and cause
current to pass through the resistors 16A and 16B as well as
resistors 16C and 16D. The passage of current through the resistors
16A and 16B will produce heat, causing the temperatures of those
resistors to tend to rise. If there is no ice on the surface 14 the
temperatures of the two resistors 16A and 16B will both rise at
substantially the same rate, so that the resistances of the two
resistors 16A and 16B will remain substantially the same. Since the
bridge B was initially balanced, if the resistances of the
resistors 16A and 16B remain the same the bridge B will remain
balanced. There will be no output across the nodes 36 and 38, and
hence the indicator 42 will not be actuated. 0n the other hand, if
there is ice on the surface 14, as indicated in FIGS. 2 and 3 at
44, the resistor 16A which is in good thermal contact with that ice
44 will remain substantially at the temperature of the ice
(0.degree. C.) unless and until the heat from the resistor 16A
melts that ice. However, the temperature of resistor 16B, thermally
insulated from the ice 44, will rise. Hence there will be a
difference between the temperatures of the two resistors 16A and
16B, that difference in resistance will unbalance the bridge B,
there will be an output across the nodes 36 and 38, that output
will be amplified by the amplifier 34, and the alarm or indicator
42 will be actuated.
Energization of the resistors 16A and 16B will continue, controlled
by the timer 28, for a period of time sufficient to detect the
presence or absence of the ice 44, after which energization of the
resistors 16A and 16B will be interrupted and those resistors will
be permitted to return to their normal temperature status, at which
time the system will be ready for another ice detection cycle, as
determined either by the timer 28 or by appropriate manual
actuation.
If the duration of a given ice detection cycle is sufficiently
limited in time, taking into account the heat-producing
characteristics of the resistor 16A, no significant quantity of the
ice 44 will be melted thereby, and the detector will thus function
to determine the presence or absence of ice whether deposited
before or after the time of initial actuation. However, if the ice
detection cycle is continued for a long enough period so that the
heat produced by the resistor 16A will melt the ice 44 on the
surface 14, the next ice detection cycle will indicate whether or
not any ice formed on the surface 14 after the preceding detection
cycle.
It will be appreciated that a significant advantage of the
disclosed ice detector is that neither a stabilized current nor a
reference voltage is required, and that the method is very reliable
since it is based on the inherent physical properties of the
detector, which are constant and which do not depend upon the
critical performance of electronic components.
While but a limited number of embodiments of the present invention
have been here specifically disclosed, it will be apparent that
many variations may be made therein, all within the scope of the
present invention as defined in the following claims.
* * * * *